Quartz glass crucible for pulling up silicon single crystal and method for producing the same

ABSTRACT

An object of the invention is to provide a quartz glass crucible reduced in the generation of vibration occurring on the surface of a silicon melt and free from the generation of rough surface and cristobalite spots, yet capable of pulling up single crystal silicon stably and at high yield even in long-term operations; it is also an object to provide a method for producing the same. In a quartz glass crucible for pulling up single crystal silicon comprising a crucible base body having a bottom part and a straight shell part with an inner layer provided to the inner surface thereof, the quartz glass crucible is characterized by that said inner layer comprises a synthetic quartz glass layer from the lowest end to at least a height of 0.25 H; a naturally occurring quartz glass layer or a mixed layer of naturally occurring quartz glass and synthetic quartz glass extended in a range of from at least 0.5 H to 0.8 H; and one selected from a synthetic quartz glass layer, a naturally occurring quartz glass layer, and a mixed quartz glass layer of naturally and synthetic quartz glass for the rest of the inner layer, wherein H represents the height from the lowest end of the bottom part to the upper end plane of the shell part. It also provides a method for producing the quartz glass crucible above.

The present invention relates to a quartz glass crucible for pulling upsingle crystal silicon, comprising a crucible base body having a bottompart and a side wall, with an inner layer provided to the inner surfacethereof.

Furthermore the invention is related to a method for producing a quartzglass for pulling up single crystal silicon comprising a crucible basebody having a bottom part and a side wall enclosing an inner cavityportion, by setting a high temperature atmosphere inside the cavityportion of the quartz glass crucible base body being attached to arotating mold, and supplying a silica powder into said high temperatureatmosphere to form an inner layer on the inner surface of the cruciblebase body by melting and vitrifying the silica powder.

Conventionally, so-called Czochralski (CZ) method is widely employedheretofore as the production method for silicon single crystals. The CZmethod comprises melting polycrystalline silicon in a crucible made ofquartz glass, immersing a seed crystal of silicon single crystal intothe silicon melt, gradually pulling up the seed crystal while rotatingthe crucible, and thereby growing the single crystal silicon from theseed crystal as core. The single crystal that is produced in said CZmethod should be of high purity and capable of producing silicon wafersat high yield; as the quartz glass crucible for use in the production,employed is a double-structured quartz glass crucible comprising aninner layer free from pores and an opaque outer layer containing pores.

With recent tendency of consuming longer time for the operation ofpulling up single crystals with increasing diameter of silicon singlecrystals, quartz glass crucibles with higher purity are required.Accordingly, the present applicants have proposed a quartz glasscrucible having a double structure comprising a transparent inner layerand an opaque outer layer, in which the inner layer is formed withsynthetic silica powder (for instance, U.S. Pat. No. 2,811,290 and U.S.Pat. No. 2,933,404, etc.). A quartz-glass crucible having an inner layermade from synthetic quartz glass is advantageous in that it is extremelylow in impurity content, suffers very low generation of surfaceroughening or cristobalite spots on the inner surface during pulling upsilicon single crystals, enables operation for a long time, andincreases the yield of pulling up single crystals.

However, in case of melting polysilicon, when compared with cruciblesmade from naturally occurring quartz, the crucibles above having innerlayers made of synthetic quartz glass tends to cause oscillation on thesurface of the melt. In particular, such surface oscillation isfrequently observed in the initial pulling up stages such as nucleation,formation of shoulders, and former stages of producing single crystalbody part; and is disadvantageous in that it lowers productivity, due toincreased time for nucleation, the generation of disordering in thecrystals, causing re-melting, i.e., the so-called melt-back, and thelike. In the light of such circumstances, the present inventors haveproposed a multi-layer structured crucible having an opaque syntheticquartz glass preliminary layer interposed between a transparent innerlayer made of synthetic quartz glass and an opaque bulk layer made ofnaturally occurring quartz glass (Japanese Patent Laid-Open No.2001-348294). However, since multi-layer structured crucible usesexpensive synthetic powder in large quantities, it suffered adisadvantage as such that it results expensive.

In the light of the aforementioned circumstances, the present inventorshave extensively conducted studies, and as a result, it has been foundthat the surface vibration generated on the surface of the silicon meltis deeply related with the inner surface of the wall (straight shellpart), and that the yield of pulling up single crystals is significantlyrelated with the inner surface of the bottom part. Furthermore, by usingnaturally occurring quartz glass or a mixture of naturally occurring andsynthetic quartz glasses for a specified part of the wall the quartzglass crucible that is used for pulling up silicon single crystals, ithas been found that the generation of vibration on the surface of thesilicon melt can be suppressed, and that it enables long stabilizedoperation using the crucible while suppressing the generation of surfaceroughening and cristobalite spots on the inner surface of the crucibleby forming a specified range of the inner layer in the vicinity of thebottom part of the crucible with synthetic quartz glass. The presentinvention has been accomplished based on these findings enabling pullingup of silicon single crystal at high yield. More specifically:

An object of the present invention is to provide a quartz glass cruciblecapable of pulling up silicon single crystal stably at high yield bysuppressing the generation of vibration on the surface of silicon melt,without generating surface roughening and cristobalite spots on theinner surface of the crucible even for long operation.

Further object of the present invention is to provide a method forproducing the quartz glass crucible above.

In order to achieve the objects above, the quartz glass crucible ischaracterized in that its inner layer comprises

-   -   a) a first part made of a synthetic quartz extending from the        bottom to at least a height of 0.25 H;    -   b) a second part made of a naturally occurring quartz glass or        made of mixed quartz glass of naturally and synthetic quartz        glass, extending in a range of from at least 0.5 H to 0.8 H;    -   c) and a residual part made of quartz glass selected from a        synthetic quartz glass, a naturally occurring quartz, or a mixed        quartz glass of naturally and synthetic quartz glass,        wherein H represents the height from the lowest side of the        bottom part to the upper end plane of the wall.

The quartz glass crucible according to the present invention is a quartzglass crucible for pulling up single crystal silicon comprising acrucible base body with an inner layer provided to the inner surface ofthe bottom an the side wall, in which said inner layer comprises, withrespect to the height (H) from the lowest end of the bottom part to theupper end plane of the side wall, a first layer which is a syntheticquartz glass layer of at least up to a height of 0.25 H; a second layermade of naturally occurring quartz glass or a mixed quartz glass ofnaturally occurring quartz glass and synthetic quartz glass extendingover a range of at least from 0.5 H to 0.8 H; and the rest of the innerlayer is formed by a residual layer consisting of one selected fromsynthetic quartz glass, a naturally occurring quartz glass, and a mixedquartz glass of naturally occurring quartz glass and synthetic quartzglass.

By providing a part (second part) of the inner layer made of naturallyoccurring quartz glass or synthetic glass containing naturally occurringglass (i.e., a naturally occurring glass mixed with synthetic glass) onthe inner surface of the crucible base body, the vibration in siliconmelt can be suppressed.

The thickness of the second part is preferably in a range of from 0.3 to3 mm. In case the thickness is less than 0.3 mm, only small effect ofsuppressing the vibration of silicon melt can be expected; a second partat a thickness exceeding 3 mm is not preferred because there is noimprovement in the effect of suppressing the vibration of the melt.

On the other hand, the yield of the silicon single crystal depends onwhether the single crystal contains dislocations or not. However, mostof the dislocations generate due to the surface roughening or to thegeneration of cristobalite spots in the later stage of the pulling upprocess, i.e., within a height of 0.25 H of the crucible that is broughtinto contact with the silicon melt for a long duration of time.Accordingly, in the quartz glass crucible according to the presentinvention, the first part of the inner layer up to a height of at least0.25 H is formed with synthetic quartz glass that is less affected bysurface roughening or generation of cristobalite spots.

The thickness of the first part of the inner layer is preferably in arange of from 0.5 to 5 mm. In case the thickness of the first partbecomes less than 0.5 mm, the effect of suppressing surface rougheningand cristobalite spots becomes small as to result in low yield. Anthickness exceeding 5 mm is also not preferred, because it increases theproduction cost.

The powder of naturally occurring silica mixed with synthetic glass forforming the inner layer of the quartz glass crucible above preferablycontains 30% or more of naturally occurring silica powder.

The quartz glass crucible for pulling up silicon single crystalsaccording to the present invention suffers less vibration of siliconmelt surface on pulling up silicon single crystals and enables stablepulling up silicon single crystals at high yield without causing surfaceroughening or generation of cristobalite spots on the inner surface ofthe crucible.

Concerning the method the above mentioned object is met by a productionmethod which is characterized in that the forming of the inner layercomprises

-   -   a) forming of a first part of the inner layer extending from the        bottom to at least a height of 0.25 H which is made of a        synthetic quartz glass;    -   b) forming of a second part of the inner layer, extending in a        range of from at least 0.5 H to 0.8 H, which is made of a        naturally occurring quartz glass or a mixed quartz glass of        naturally and synthetic quartz glass;    -   c) forming of a residual part of the inner layer, made from a        quartz glass selected from a synthetic quartz glass, a naturally        occurring quartz glass, and a mixed quartz glass of naturally        and synthetic quartz glass,        wherein H represents the height from the lowest end of the        bottom part to the upper end plane of the wall.

A first part of the inner layer is formed to at least a height of 0.25 Hby supplying synthetic silica powder in a high temperature atmosphereand by melting and vitrifying the powder. Followed by moving upward,downward, or to the right or left, if necessary, a silica powder supplynozzle that has been used for supplying the synthetic silica powder, andthen forming, over a height range of at least 0.5 H to 0.8 H, a secondpart of the inner layer consisting of naturally occurring quartz glassor of naturally occurring quartz glass mixed with synthetic quartzglass, This is achieved by supplying a powder of naturally occurringsilica or of naturally

Here and in the following “H” represents the height from the lowest endof the bottom part to the upper end plane of the side wall as it isshown in more detail in FIG. 1.

-   -   occurring silica mixed with synthetic silica from the supply        nozzle.

Alternatively the second part of the inner layer is produced first bymelting and vitrifying a powder of naturally occurring silica or ofnaturally occurring silica mixed with synthetic silica that is suppliedfrom a silica powder supplying nozzle, followed by moving, if necessary,upward, downward, or to the right or left the silica powder supplynozzle and then forming the first part of the inner layer, which is asynthetic quartz glass layer having a height of at least a 0.25 H fromthe lowest end of the outer surface of the bottom part by melting andvitrifying the synthetic silica powder supplied from the silica powdersupplying nozzle.

In a preferred d method a preliminary quartz glass layer is formed overthe entire inner surface of the crucible base body by melting andvitrifying a silica powder which is a synthetic silica powder, wherebythe second part of the inner layer is formed over a height range of from0.5 H to 0.8 H is formed by coating the preliminary layer with a secondquartz glass layer made from naturally occurring silica powder or apowder of naturally occurring silica mixed with synthetic silica.

Alternatively a preliminary quartz glass layer is formed over the entireinner surface of the crucible base body by melting and vitrifying asilica powder which is a naturally occurring silica powder or a powderof naturally occurring silica mixed with synthetic silica powder,whereby the first part of the inner layer is formed over a height rangeto at least 0.25 H is formed by coating the preliminary layer with asecond quartz glass layer made from synthetic silica powder.

The quartz glass crucible can be produced by a simple production methodcomprising supplying a synthetic silica powder, a naturally occurringsilica powder, or a mixed powder of naturally occurring silica andsynthetic silica to each of the portions of the crucible base, and thenmelting and vitrifying each of the powders for forming the several partsof the inner layer.

The present invention is described more specifically below by way ofexamples, but it should be understood that the present invention is notonly limited thereto.

FIG. 1 shows a schematically drawn cross section view of the quartzglass crucible of the present invention.

FIG. 2 is a schematic drawing of the method for producing the quartzglass crucible of the present invention.

The structure of the quartz glass crucible according to the presentinvention is shown in FIG. 1.

In FIG. 1 are shown a quartz glass crucible 1, bottom part 2 of thecrucible, side wall 3 forming a straight shell and inner layer 4,consisting of a first part which is a synthetic quartz glass layer 5, asecond part, which is a layer 6 made of naturally occurring quartz glass(or alternatively it is made of naturally occurring glass mixed withsynthetic glass) and a residual layer at the upper end and between firstpart 5 and second part 6.

FIG. 2 shows the method for producing the quartz glass crucibleaccording to the invention.

In FIG. 2 are shown a rotating mold 7, a crucible base body 8, a meansfor supplying silica powder 9, a plate-like lid body 10, a flow controlvalve 11, a power supply 12, an arc electrode 13, a silica powder supplynozzle 14, and high temperature atmosphere 15.

The quartz glass crucible according to the present invention is formedby introducing naturally occurring silica powder from the silica powdersupply means 9 into the rotating mold 7, shaping the powder into theform of the crucible, inserting the arc electrode 13 therein, andcovering the aperture part of the body shaped into the crucible with aplate-like lid body 10, and thus, by using the arc electrode 13, atranslucent crucible base body 8 is formed by setting the inside cavityof the crucible-like shaped body to a high temperature gaseousatmosphere and thereby melting and vitrifying at least a partially theinside of the crucible-like shaped body.

Then, a first silica powder is supplied into the high temperatureatmosphere 15 from the silica powder supply means 9 while controllingthe supply rate with the flow control valve 11 to thereby form a quartzglass inner layer at the desired position by melting and vitrifying thepowder.

Subsequently, a synthetic silica powder is supplied to the hightemperature atmosphere 15 from the silica powder supply nozzle 14, and,on forming a quartz glass layer (first part 5) at the desired positionby melting and vitrifying the thus supplied silica powder, therebyforming a synthetic quartz glass inner layer 5 up to a height of 0.25 Hfrom the lowest end of the outer surface of the bottom part. “H”represents the height from the lowest end of the bottom part to theupper end plane of the side wall.

In the same way and by using naturally occurring quartz glass powder, asecond part 6 of the inner is formed on the wall in a range from 0.5 Hto 0.8 H consisting of naturally occurring quartz glass layer.

The rest of the inner layer 4 is formed with one kind of quartz glassselected from a synthetic quartz glass, a naturally occurring quartzglass, or a naturally occurring quartz glass mixed with synthetic quartzglass.

There are several preferred production methods such as

-   -   (i): a method comprising forming a first part of the inner        quartz glass layer to at least a height of 0.25 H by supplying        synthetic silica powder in a high temperature atmosphere and by        melting and vitrifying the powder, followed by moving upward,        downward, or to the right or left, if necessary, the silica        powder supply nozzle 14 that has been used for supplying the        synthetic silica powder, and forming, over a height range of at        least 0.5 H to 0.8 H a naturally occurring quartz glass powder        or a mixture of naturally occurring quartz glass and synthetic        quartz glass 6 from the nozzle 14 in order to produce the second        part 6 of the inner layer 4;    -   (ii) a method comprising forming the second part 6 of the inner        layer 4 over a height range of at least 0.5 H to 0.8 H by        melting and vitrifying a powder of naturally occurring silica or        of naturally occurring silica mixed with synthetic silica that        is supplied from a silica powder supplying nozzle 14, followed        by moving, if necessary, upward, downward, or to the right or        left the silica powder supply nozzle 14, and then forming the        first part 5 of inner layer 5 to at least a height of 0.25 H        from the lowest end of the outer surface of the bottom part by        melting and vitrifying synthetic silica powder supplied from the        silica powder supplying nozzle 14; and    -   (iii) a method comprising forming a preliminary quartz glass        inner layer over the entire inner surface of the crucible base        body by melting and vitrifying a first silica powder supplied        from the silica powder supply nozzle 14, followed by forming a        second quartz glass inner layer on the desired position by        supplying a second silica powder.

In the production method (iii), preferred are to use synthetic silicapowder for the first powder and a naturally occurring silica powder or apowder of naturally occurring silica mixed with synthetic silica for thesecond powder, such that the second part of the inner layer 6 made ofnaturally occurring quartz glass or of naturally occurring quartz glassmixed with synthetic quartz glass is formed over a height range of from0.5 H to 0.8 H.

EXAMPLE 1

By using the apparatus shown in FIG. 2, high purity naturally occurringsilica powder subjected to purification treatment was fed into arotating mold 7, and the powder was formed into a quartz glasscrucible-like shape by the centrifugal force. Then, an arc electrode 13was inserted into the quartz glass crucible base body, the aperture partwas covered with a platy lid body 10, and a high temperature gaseousatmosphere was provided inside the inner cavity by using the arcelectrode 13 to melt and vitrify the base body. Thus, a translucentquartz glass crucible base body 8 was formed by cooling the molten andvitrified body. Then, after setting high temperature atmosphere 15inside the inner cavity of the translucent quartz glass crucible basebody 8 by means of arc electrode 13 while rotating the mold 7, syntheticsilica powder was supplied therein at a rate of 100 g/min from thesilica powder supply nozzle 14. In this manner, a synthetic quartz glassinner layer 5 about 2 mm in thickness was molten and joinedmonolithically with the inner surface of the translucent crucible basebody 8 to a height of at least 0.4 H from the lowest end of the outersurface of the bottom part, where H represents the height from thelowest end of the bottom part to the upper end plane of the shell part.Then, the silica powder supply nozzle 14 was moved upward, and bysupplying a powder of naturally occurring silica at a rate of 100 g/minfrom a silica powder supply means 9, a naturally occurring quartz glassinner layer 6 about 2 mm in thickness was molten and joinedmonolithically with the inner surface of the translucent crucible basebody 8 over a height range of 0.4 H to 1.0 H. The diameter of the thusobtained quartz glass crucible was 24 inches. On pulling up singlecrystal according to CZ method by filling the quartz glass crucible withpolycrystalline silicon and melting, perfect single crystal was obtainedafter operation of about 90 hours without generating any vibration onthe surface of silicon melt

EXAMPLE 2

High purity naturally occurring silica powder subjected to purificationtreatment was fed into a rotating mold to form the powder into a quartzglass crucible-like shape by the centrifugal force. Then, an arcelectrode was inserted into the quartz glass crucible body, the aperturepart was covered with a platy lid body, and a high temperature gaseousatmosphere is provided inside inner cavity by using the arc electrode.Thus, a translucent quartz glass crucible base body was formed bycooling the molten and vitrified base body. Then, after setting hightemperature atmosphere inside the translucent quartz glass crucible basebody by means of arc electrode while rotating the mold, synthetic silicapowder was supplied therein at a rate of 100 g/min from the silicapowder supply nozzle. In this manner, a synthetic quartz glass innerlayer about 2 mm in thickness was molten and joined monolithically withthe inner surface of the translucent crucible base body. Subsequently,about 0.8 mm thick inner layer of naturally occurring quartz glass mixedwith synthetic quartz glass was formed on the inner layer over a heightrange of 0.45 H to 0.9 H of the crucible base body by supplyingsynthetic silica powder at a rate of 50 g/min from the silica supplymeans 9 and naturally occurring silica powder at a rate of 50 g/min fromthe predetermined position through the silica supply nozzle above. Thediameter of the thus obtained quartz glass crucible was 24 inches. Onpulling up single crystal according to CZ method by filing the quartzglass crucible with polycrystalline silicon and melting, perfect singlecrystal was obtained after operation of about 90 hours withoutgenerating any vibration on the surface of silicon melt.

COMPARATIVE EXAMPLE 1

By using the apparatus shown in FIG. 2, high purity naturally occurringsilica powder subjected to purification treatment was fed into arotating mold 7, and the powder was formed into a quartz glasscrucible-like shape by the centrifugal force. Then, an arc electrode 13was inserted into the quartz glass crucible base body, the aperture partwas covered with a platy lid body 10, and a high temperature gaseousatmosphere was provided inside the inner cavity by using the arcelectrode 13 to melt and vitrify the base body Thus, a translucentquartz glass crucible base body 8 was formed by cooling the molten andvitrified body. Then, after setting high temperature atmosphere 15inside the inner cavity of the translucent quartz glass crucible basebody 8 by means of arc electrode 13 while rotating the mold 7, syntheticsilica powder was supplied therein at a rate of 100 g/min. In thismanner, a synthetic quartz glass inner layer about 2 mm in thickness wasmolten and joined monolithically with the inner surface of thetranslucent crucible base body 8. The diameter of the thus obtainedquartz glass crucible was 24 inches. On pulling up single crystalaccording to CZ method by filling the quartz glass crucible withpolycrystalline silicon and melting, vigorous vibration was generated onthe surface of the silicon melt to find seeding operation andconsecutive operations unfeasible.

COMPARATIVE EXAMPLE 2

By using the apparatus shown in FIG. 2, high purity naturally occurringsilica powder, subjected to purification treatment was fed into arotating mold 7, and the powder was formed into a quartz glasscrucible-like shape by the centrifugal force. Then, an arc electrode 13was inserted into the quartz glass crucible base body, the aperture partwas covered with a platy lid body 10, and a high temperature gaseousatmosphere was provided inside the inner cavity by using the arcelectrode 13 to melt and vitrify the base body. Thus, a translucentquartz glass crucible base body 8 was formed by cooling the molten andvitrified body. Then, after setting high temperature atmosphere 15inside the inner cavity of the translucent quartz glass crucible basebody 8 by means of arc electrode 13 while rotating the mold 7, naturallyoccurring silica powder was supplied therein at a rate of 100 g/min. Inthis manner, a naturally occurring quartz glass inner layer about 2 mmin thickness was molten and joined monolithically with the inner surfaceof the translucent crucible base body 8. The diameter of the thusobtained quartz glass crucible was 24 inches. On pulling up singlecrystal according to CZ method by filling the quartz glass crucible withpolycrystalline silicon and melting, perfect crystal was foundunfeasible because disordering is generated on the single crystal afterpassage of about 50 hours, although no vibration is generated on thesurface of the silicon melt.

1. A quartz glass crucible for pulling up single crystal silicon, saidcrucible comprising a crucible base body having a bottom part having alowest side and a side wall having an upper end plane, and an innerlayer provided on an inner surface thereof, wherein said inner layercomprises a) a first part made of a synthetic quartz extending from thebottom to at least a height of 0.25 H; b) a second part made of anaturally occurring quartz glass or made of mixed quartz glass ofnaturally occurring and synthetic quartz glass, and extending in a rangeof from at least 0.5 H to 0.8 H; and c) a residual part made of quartzglass selected from the group consisting of synthetic quartz glass,naturally occurring quartz, and mixed quartz glass of naturally andsynthetic quartz glass, wherein H represents a height from the lowestside of the bottom part to the upper end plane of the wall.
 2. A quartzglass crucible according to claim 1, wherein the mixed quartz glass ofnaturally occurring quartz glass and synthetic quartz glass is formedusing a mixed powder of naturally occurring silica and synthetic silicain which the naturally occurring silica accounts for 30% or higher ofthe mixed powder.
 3. A quartz glass crucible according to claim 1,wherein the second part has a thickness in a range of from 0.3 to 3 mm.4. A quartz glass crucible according to claim 1, wherein the first parthas of the inner layer has a thickness in a range of from 0.5 to 5 mm.5. A method for producing a quartz glass crucible for pulling up singlecrystal silicon, said method comprising forming a crucible base bodyhaving a bottom part and a side wall enclosing an inner cavity portion,by setting a high temperature atmosphere inside the cavity portion ofthe quartz glass crucible base body attached to a rotating mold, andsupplying a silica powder into said high temperature atmosphere to forman inner layer on an inner surface of the crucible base body by meltingand vitrifying the silica powder, the forming of the inner layercomprising: a) forming of a first part of the inner layer extending fromthe bottom to at least a height of 0.25 H, said first part being made ofa synthetic quartz glass; b) forming of a second part of the innerlayer, extending in a range of from at least 0.5 H to 0.8 H, said secondpart being made of a naturally occurring quartz glass or a mixed quartzglass of naturally occurring and synthetic quartz glass; c) forming of aresidual part of the inner layer, said residual part being made from aquartz glass selected from the group consisting of synthetic quartzglass, naturally occurring quartz glass, and mixed quartz glass ofnaturally and synthetic quartz glass, wherein H represents a height froma lowest end of the bottom part to an upper end plane of the wall.
 6. Amethod according to claim 5, wherein, for supplying the silica powderinto the high temperature atmosphere, a supplying nozzle is used, bywhich synthetic silica-powder is supplied to a first part of thecrucible base body to form the inner layer on the bottom part of thecrucible base and in a vicinity thereof, and then moving the supplynozzle to supply naturally occurring silica powder or a mixed powder ofnaturally occurring silica or synthetic silica to a second part separatefrom the first part, to form the second part of the inner layer on thecrucible base body.
 7. A method according to claim 5, wherein the innerlayer is produced by forming a preliminary quartz glass layer on theentire inner surface of the crucible base body by supplying a firstsilica powder into the high temperature atmosphere, the first silicapowder being naturally occurring silica powder or a mixed powder ofnaturally occurring silica and synthetic silica, and melting andvitrifying the first silica powder, and then forming the first part ofthe inner layer by supplying, melting and vitrifying a synthetic silicapowder.
 8. A method according to claim 5, wherein the inner layer isproduced by forming a preliminary quartz glass layer on the entire innersurface of the crucible base body by supplying a synthetic silica powderinto the high temperature atmosphere and melting and vitrifying thesynthetic silica powder, and then forming the second part of the innerlayer by supplying, melting and vitrifying a silica powder which isnaturally occurring silica powder or a mixed powder of naturallyoccurring silica and synthetic silica.